Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$23.42	9.167%	$25.5669	$25.57	$25.55	$25.60
Purchase #2	$235.29	12.628%	$265.0024	$265.00	$265.00	$265.00
Purchase #3	$218.30	12.387%	$245.3408	$245.34	$245.35	$245.30
Purchase #4	$51.88	13.801%	$59.04	$59.04	$59.05	$59.00
Purchase #5	$213.61	6.278%	$227.0204	$227.02	$227.00	$227.00
Purchase #6	$123.85	7.136%	$132.6879	$132.69	$132.70	$132.70
Purchase #7	$45.68	7.762%	$49.2257	$49.23	$49.25	$49.20
7 purchase totals =	$912.03		$1,003.8841	$1,003.89	$1,003.90	$1,003.80